Conventional gas fired air impingement tunnel ovens are configured for directing a burner flame into an inaccessible or difficultly accessed low air pressure zone or air volume within the interior of the oven's baking case. Such low pressure zone is typically laterally bounded by the oven's lateral wall, and is oppositely laterally bound by an air plenum which effectively longitudinally partitions the oven's interior. In operation of such tunnel ovens, safety concerns require that the supply of combustible gas (typically natural gas or propane) to the burner be terminated upon extinguishment of the burner's flame.
To insure gas cutoff upon flame extinguishment, a gas cutoff valve is typically electronically controlled by an electronic control unit which is capable of receiving and being actuated by a termination or cessation of an ongoing electrical signal current. To generate such a signal to such controller, a pair of metal electrodes are known to be mounted and extended into such low pressure air volume within the baking case, such electrodes being positioned to intersect the path of the gas flame emanating from the burner. Upon maintenance of voltage or an electrical potential difference between such electrodes, a circuit including such electrodes is completed as a result of a micro-electroconductivity character of the flame.
Electric current from such completed flame incorporating electric circuit is commonly and conventionally utilized for maintaining an input signal to the electronic controller. While a burner flame is present, and during ongoing completion of such electrical circuit, the electronically controlled burner cutoff valve is maintained by the controller at an open position. Alternatively, upon flame extinguishment and a resultant breaking of the signal circuit, such valve is actuated by the controller to close and cutoff gas supply.
A problem or defect of such electrode dependent flame sensors is recognized as resulting from deposits of solid foreign matter from the combustible gas and flame onto the electrodes. Such solids cumulatively build up over time, and such solids tend to undesirably function as a resistor or dielectic acting as an insulator which interferes with flame conducted passage of electrical current from one electrode to the other. Upon such build up of such insulating solids, the oven's controller unit interprets a resultant interruption of current as a flame extinguishment event, and prematurely cuts off gas to the burner, unnecessarily shutting down operation of the oven.
Upon an accumulation of such insulating solids upon flame sensing electrodes, access to the oven's low pressure air volume which resides between the oven's lateral wall and plenum must be gained for electrode maintenance and electrode interchange. Such interior space of such oven typically cannot be achieved by a commercial oven user, requiring a service call by a technician or oven mechanic. Thus, flame sensing electrode fouling results in undesirable “down time” effecting usage of the oven and negatively impacting the operation of a commercial restaurant utilizing the oven.
The instant inventive air impingement tunnel oven solves or ameliorates the problems, defects, and deficiencies described above by replacing flame path mounting electrodes with a specially configured optical flame sensing assembly.